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A link between galaxy clusters and dark matter

An article published in the journal “Physical Review Letters” offers clues about the link between the internal structure of a galaxy cluster and the dark matter environment surrounding it. The study of dark matter is complex because it can only be done indirectly due to the fact that we can’t detect it directly. Until now, scientists believed that the greater the mass of a cluster the greater the amount of dark matter in its environment. This new research suggests that things are more complicated.

Hironao Miyatake of NASA’s JPL led the team that carried out this research examining about 9,000 galaxy clusters included in the Sloan Digital Sky Survey’s DR8 catalog. They were divided into two groups according to their internal structure: clusters in which galaxies are diffuse were included in a group while those in which they are close to each other were included in the other group.

The team used the technique of gravitational lensing to verify how the galaxy clusters examined bent the light from other objects with their force of gravity to ensure that the two groups had similar masses. This was confirmed yet a comparison between the two groups showed a difference in the distribution of galaxy clusters.

Normally these clusters are separated from their neighbors average by an average of about 100 millions of light years. However, the clusters containing galaxies close together have fewer neighbors clusters. According to the scientists who conducted this research, this difference is due to different dark matter environments in which the groups of clusters formed.

This result confirms the predictions of current theories on the origin of the universe. Immediately after the Big Bang there was a very short period known as cosmic inflation and subsequently small quantum fluctuations that caused a non uniform distribution of matter. The link between the internal structure of galaxy clusters and the distribution of dark matter that surrounds them is a consequence of those fluctuations.

Given the importance of these studies of galaxy clusters, the research will continue. Masahiro Takada, another of the scientists who participated in the exam of the galaxy clusters, stated that the data of another survey, carried out using the Subaru Telescope’s Hyper Suprime-Cam, will be used for further verification. The hope is also to obtain new details about the evolution of galaxy clusters, the history of the birth of the universe and dark matter and energy.